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Chapter 3:Cell Biology

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III. P

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• Terminology– Intracellular: (Intra- Inside) inside the cell– Extracellular: (Extra- Outside) outside of the cell– Intercellular: (Inter- Between) from 1 cell to another– Glycoproteins: carb’s + proteins– Glycolipids: Carb’s + Lipids– Membrane Potential: result of uneven distribution of ions on the

inside verses the outside of the cell

• Glycocalyx:– Collection of glycoproteins, glycolipids, and carb’s that lies on the

outer surface of the plasma membrane

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IV. Membrane Lipids

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IV. M

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ds• Phospholipids (PL’s):

– Predominant lipid in membrane

– Bipolar:• Hydrophilic “head” is water

loving and polar and faces both surfaces (inner & outer)

• Hydrophobic “tail” is water hating and non-polar and crowd together between the heads

• Cholesterol– Makes up 1/3 of the

membrane and lie btwn PL’s– Helps to limit PL’s mvmt

providing stability for the PM– It is also bipolar and the “tail”

is embedded in head while the ring is embedded in the tails

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IV. Membrane Lipids

• *Fluid Mosaic Model*– The lipid bilayer is mobile with things floating

w/in it– Consequences of this:

a) Important for molecule distribution in the membrane

b) Slight damage can be repaired because the PL’s will move to cover it

c) It enables two different membranes to fuse with each other

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V. Membrane ProteinsA. Marker Molecules

B. Attachment Proteins

C. Transport Proteins

D. Receptor Proteins

E. Enzymes

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V. Membrane Proteins (MP)

• Many fxns of the plasma membrane are determined by the combination of membrane proteins present.

• The ability of these proteins to fxn properly is determined by their 3-D shape

• There are 2 major types:1. Integral/Intrinsic

• (Transmembrane) contain hydrophobic and hydrophilic regions to match the phospholipids characteristics & location

2. Peripheral/Extrinsic• Surface proteins on inner or outer surface.• Can be bound to an integral protein or the phospholipids head

• There are 5 major classes of MP’s

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5 major classes of Membrane proteins

I. Markermolecules

II. AttachmentProteins

III. TransportProteins

IV. ReceptorProteins

V. Enzymes

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Membrane Proteins: I. Marker Molecules

• Glycoproteins or glycolipids that allow for cells to identify other cells or other molecules

• Important because cells aren’t isolated and must function as a whole for normal body function.

• May be integral or peripheral proteins

• Ex/ immune cells

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Membrane Proteins: II. Attachment Proteins

• Integral proteins that may attach to intracellular molecules.

• Integrins can also function in cellular communication.

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Membrane Proteins: III. Transport Proteins

All exhibit 3 characteristics

1. Specificity– Each binds to & transports

only 1 types of molecule/ion

2. Competition– Closely related substances

may bind to the same binding site & the one w/ greater [ ] or higher affinity is more readily moved across the PM

3. Saturation– Movement is limited by the #

of transport proteins rate will eventually plateau because the # of proteins are going at their maximum rate

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Membrane Proteins: III. Transport Proteins

A. Channel Proteins• Form passageways through the

plasma membranes that have both hydrophobic and hydrophilic regions.

B. Carrier Proteins• Move larger ions or molecules

across the membrane, when bound it changes shape to allow it to move from one side of the membrane to the other then return to its original shape to work again.

C. ATP-powered pumps• Moves ions or molecules across the

membrane using ATP.

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Membrane Proteins: III. Transport Proteins

A. Channel Proteinsa. Non-gated Channels

• Always open responsible for the permeability of the plasma membrane when the cell membrane at rest.

b. Gated Channels• Can be opened or closed

i. Ligand Gated – Small molecules must bind in

order to open or close the channel

ii. Voltage Gated– Change in voltage across the

plasma membrane causes the gate to open

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Membrane Proteins: III. Transport Proteins

B. Carrier Proteinsa. Uniporter

• Movement of 1 ion or molecule across the plasma membrane.

b. Symporter• Movement of 2 ions or molecules in

the same direction (into the cell or out of the cell).

c. Antiporter• Movement of 2 ions or molecules in

opposite directions (one in and one out or vise versa).

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Membrane Proteins: III. Transport Proteins

C. Sodium-Potassium Pump• These have 2 binding sites.

One is for the molecule to be moved the other is for ATP

• Breakdown of ATP releases e+ Ding shape of the “pump” protein which moves the molecule across the membrane

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Membrane Proteins: IV. Receptor Proteins

• Proteins or glycoproteins in the plasma membrane that have an exposed receptor site on the outer cell surface which can attach to specific chemical signals.

• Many are part of an intercellular communication system that coordinates cell activities.

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Membrane Proteins: IV. Receptor Proteins

A. Receptor linked to channel proteins

– These help form ligand-gated channels & when bound it changes the channels shape to move ions

B. Receptors linked to G-protein complexes

– Uses a second messenger system, binding of the receptor externally causes to the cell internally

• 3 ways a can stimulate a cellular response

1. Intracellular chemical signals

2. Opening channels in the plasma membrane

3. Activation of enzymes associated with the plasma membrane

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Membrane Proteins: V. Enzymes

• These may work on the inner or outer surface of the plasma membrane.

• Some are always active but others are activated by things like GPCR’s

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VI. Movement through the plasma membrane

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V. Mvmt thru the PM• Inside of the cell:

– Enzymes other proteins, glycogen, high potassium concentration• Outside of the cell:

– High concentration of sodium, calcium, & chloride• The cell has to be able to bring in nutrients inside and get waste

products out without changing the cell’s volume, because too much can cause the cell the rupture (causing cell death) or to shrivel (also causing cell death).

• Movement1. Molecules that are lipid soluble or very small water soluble molecules

will freely go across the plasma membrane.

2. Large lipid soluble molecules and water soluble molecules can’t pass through the plasma membrane and may need to use transport proteins.

3. Larger water soluble molecules or whole cells may be moved by vesicles.

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Membrane transport mechanisms

A. Passive Transport Mechanisms• No energy required to move

molecules from one side of the membrane to another

B. Active Transport Mechanisms• Energy required to move

molecules from one side of the membrane to another

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Membrane transport mechanisms

Passive Transport Mechanisms

A. Diffusion

B. Osmosis

C. Facilitated Diffusion

Active Transport Mechanisms

A. Active Transport

B. Secondary Active Transport

C. Vesicular Transporta. Endocytosis

b. Exocytosis

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Passive Transport MechanismsA. Diffusion:

– Movement of solutes from an area of high concentration to an area of low concentration

– Concentration gradient: concentration difference between 2 points divided by the distance between the 2 points,

– Rate of Diffusion1. Magnitude of the concentration gradient

2. Temperature of the solution

3. Size of the diffusion molecules

4. Viscosity of the solvent

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Passive Transport MechanismsB. Osmosis

– Diffusion of water across a selectively permeable membrane

– Will allow water but not all solutes with in the water

– Important because it can influence a cell’s function when water moves.

– Osmotic Pressure:• Force required to prevent water

movement across a selectively permeable barrier via osmosis

1) Isosmotic

2) Hyperosmotic

3) Hyposmotic

Concentration of solutions

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Passive Transport MechanismsB. Osmosis

• Tonicity: refers to the cell’s shape remaining constant b/c it maintains it’s internal pressure

1. Isotonic sol’n: no net mvmt of H2O, cell doesn’t D shape

2. Hypertonic sol’n: mvmt out of cell b/c sol’n has a greater [ ] of solute thus a higher osmotic pressure (crenation)

3. Hypotonic sol’n: mvmt into cell b/c sol’n has a lower [ ] of solute thus a lower osmotic pressure (Lysis)

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Passive Transport MechanismsC. Facilitated Diffusion

– Amino acids & glucose go into the cell and area going out of the cell can’t occur via direct diffusion because they are too big. Thus there is

– Mediated transport (facilitated diffusion):• Process by which transport proteins assist the movement of

water soluble molecules or electrically charged molecules or ions across the plasma membrane.

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Active Transport Mechanisms

A. Active Transport• also a type of mediated

transport. Requires energy provided by ATP movement dependent on the number of pumps and availability of ATP.

• Important because it can move things against their concentration gradients.

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Active Transport Mechanisms

B. Secondary Active Transport

• Passive transport of 1 molecule with its concentration gradient helps to energize the carrier so that it can transport the second molecule against its concentration gradient.

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Active Transport Mechanisms

C. Vesicular Transport• Movement of larger

volumes of substances across the plasma membrane through the formation and release of vesicles requiring ATP.

• BUT…the specificity seen in others doesn’t occur in this process. a. Endocytosis

i. Pinocytosis

ii. Phagocytosis

iii. Receptor mediated endocytosis

b. ExocytosisUnit 1 29

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Active transport mechanismsa) Endocytosis: uptake

of material into the cell.

• 3 types:i. Pinocytosis

• Molecules dissolved in liquid

ii. Phagocytosis• Cells and solid

particles

iii. Receptor mediated endocytosis

• Specificity for substances

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Active Transport Mechanisms

b. Exocytosis– Materials

manufactured by the cell are packaged in secretory vesicles that fuse w/the PM & release their contents outside of the cell

– ATP req’d– Proteins & other water

soluble substances

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